Toyota announced on Wednesday that it will pay more than $1 billion to settle a class-action lawsuit involving some of its vehicles speeding up with no warning. The settlement, which is the largest in U.S. history involving automobile defects, covers payouts to cover the loss of value for former owners, extended warranties, and the installation of brake-override systems in up to 3.25 million vehicles. Disturbingly, after several recalls and studies, it’s still unclear what caused the problem, which led to several accidents and killed at least four people. Toyota, which denies that the problem was caused by flaws in its electronic throttle-control system, doesn’t admit fault or unlawful conduct in the settlement. “We have not resolved the issue of is there a bug,” says Steve W. Berman, a lawyer for the plaintiff.